This invention relates generally to completion methods of subterranean wells and more particularly to methods and means for completing poorly consolidated formations whereby sand production is eliminated or reduced.
Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, i.e., a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. Once a wellbore has been drilled, the well must be completed; a completion involves the design, selection, and installation of equipment and materials in or around the wellbore for conveying, pumping, or controlling the production or injection of fluids. After the well has been completed, production of oil and gas can begin.
Hydraulic fracturing is a primary tool for improving well productivity by placing or extending channels from the wellbore to the reservoir. This operation is essentially performed by hydraulically injecting a fracturing fluid into a wellbore penetrating a subterranean formation and forcing the fracturing fluid against the formation strata by pressure. The formation strata or rock is forced to crack and fracture. Proppant is placed in the fracture to prevent the fracture from closing and thus, provide improved flow of the recoverable fluid, i.e., oil, gas or water.
Where the formation is “soft” or poorly consolidated, small particulates typically of sand present in the formation may travel with the hydrocarbons. Such a production of sand is highly undesirable since it erodes surface and subterranean equipment, requires a removal process before the hydrocarbon can be process and eventually, counteracts the suitable effects of stimulation techniques such as acid stimulation.
The most common approach to minimize flow of small particulate is to filter the produced fluids through a gravel pack retained by a screen. The produced fluids travel through the gravel pack and the screen without substantially reducing the production before entering the wellbore while the smaller particulates are blocked. However, this technique is relatively onerous and with time, the gravel and the screen may be plugged by scale or eroded by the sand.
This explains the development of so-called screenless completion techniques. These techniques typically involve the injection of a consolidating fluid including a resin, a curing agent, a catalyst and an oil wetting agent. The resin sets in the formation, consolidating it and reducing the concentration of free small particulates. Examples of consolidating fluids and of methods for their use are reported for instance in their use U.S. Pat. Nos. 5,806,593; 5,199,492; 4,669,543; 4,427,069; and 4,291,766.
Conventional consolidating fluids tend to have relatively long setting times. Therefore, the fluids tend to keep flowing into the areas of least resistance, leaving the others untreated. This drastically limits the length of wellbore that can be treated in a single application to no more than about 6 meters (20 feet). Further, poor results are achieved with heterogeneous formations consisting for example of layers having different permeabilities. Resin-based consolidation systems are known to be very complicated to apply, for instance requiring up to five treatment stages and often raise environmental issues.
In an effort to obviate the disadvantages of conventional fluids, multiple wells treatments have been proposed. Most of them include either an emulsion or a foam. U.S. Pat. No. 5,363,917 teaches a foamed consolidating fluid which can support combustion of hydrocarbons in the formation. Products of the hydrocarbon combustion consolidate the formation. U.S. Pat. Nos. 5,010,953 and 5,567,088 disclose a consolidating fluid provided as an aerosol in steam. The former patent teaches that steam maintains void spaces in the formation during setting of a polymerizable compound, e.g. furfuryl alcohol. U.S. Pat. No. 6,364,020 teaches emulsions comprising at least two discontinuous phases comprising a gelling polymer, such as a polysaccharide, in one phase and an inorganic or organic crosslinker in another.
Different methods of completing an unconsolidated formation with or without a consolidation treatment are known. U.S. Pat. No. 5,551,514 proposes a multi-stage consolidation followed by a hydraulic fracturing treatment in which proppant flowback control techniques are employed. U.S. Pat. No. 6,450,260 describes a method of performing the technique patented in U.S. Pat. No. 5,551,514, using a flexible gel system.
Other methods to minimize sand production involve determining the direction of fracture propagation and orienting or shaping perforations (See U.S. Pat. Nos. 5,386,875 and 6,283,214). U.S. Pat. No. 6,431,278 defines a curve that correlates the percentage of flow through out-of-phase perforations with the fracture conductivity over formation permeability. Given a desired production flow, formation conductivity may be defined. This allows the well operator to design and perform a fracturing operation to achieve the conductivity necessary to produce the well below the critical drawdown pressure for sand production.
Though some successes have been obtained with most of the above-mentioned techniques, none of them has achieved large commercial acceptance, in particular in view of the technical and cost limitations.
It is therefore an object of the present invention to provide an improved method of completing an unconsolidated interval.